Production of trimesic acid



United States Patent PRODUCTION OF TRIMESIC ACID William G. Toland, San Rafael, 'Califi, assignor to California Research Corporation, San Francisco, Calif., a corporation of Delaware No Drawing. Application October 4, 1956 Serial No. 613,844

2 Claims. (Cl. 260-524) This invention relates to a process for producing un- 2,876,257 Patented Mar. 3, 1959 lCC isophthalic and tereph'thalic acids. The filter cake, recovered from the filtration of the acidified oxidation product and -weighing25.8 g., was'extracted with hot water and, on cooling, g. of a solid organic. acid material'was collected (neutral equivalent.7 6.6). Of this material,'-5.'5. g. was trimesic acid and the remainder isophsubstituted benzene polycarboxylic acids, more particularly it relates to a process in which a tetrasubstituted benzene is oxidized to give a benzene polycarboxylic acid product mixture containing a substantial proportion of 1,3,5-benzene tricarboxylic acid (trimesic acid).

This application is a continuation-ih-part of'rny 'copending application Serial No. 369,541, filed July 21, 1953, now abandoned.

It hasbeen found that substituted benzenes having at least three substituents attached to the benzene nucleus by a carbon to carbon bond and having at least two of fthe substituents in ortho-relationship to each other, may be oxidized to produce an unsubstituted benzene polycarboxylic acid having a number of carboxyl groups smaller than the number of said substituents by introducing the polysubstituted benzene, together with, 1) a water-soluble sulfate, (2) elemental sulfur or a'sulfur compound containing sulfur at a valence below plus 6, and, (3) water into a reaction zone and there heating the mixture to a temperature above 500 F.

In particular, isodurene, a tetramethyl benzene having its methyl substituents in positions 1, 2, 3 and 5 on the benzene nucleus, so that at least two of these substituents are present in ortho-relationship to each other, and obtained in any suitable manner, for instance, from the BF /HF catalyzed isomerization of durene, can be oxidized in accordance with the aforementioned oxidation process and yields an aromatic acid product mixture'containing a substantial amount of trimesic acid, as shown in the following Example 1.

EXAMPLE I illustrated by Example II.

clave was sealed, its contents heated to 625 F. and.

maintained at this temperature with constant shaking for two hours. The final pressure on the autoclave recorded at that time'was 2400 p. s. i. g. When the heat was turned off and the contents of the autoclave cooled to room temperature, reactor gases were bled through a caustic scrubber where about 10 g. of H S was absorbed. The remaining product mixture was steam-stripped-to eliminate H S and free ammonia and filtered to separate sulfur, if any were present in the oxidation reaction. The mixture was then saponified with caustic andacidified with dilute HCl to a pH of about 1.0 and filtered cold. The filtrate was evaporated to dryness, andthe remaining solid material was slurried with methanol, whereupon dry HCl gas was passed through the slurry. The resulting ester solution was distilled to remove methanol, and the residue extracted with ether anddried to leave-4.3 got a solid ester mixture whichv hadasaponilfication equivalent of 90.0. Its'trimesic acid content was "1.8 g., the remaining acids (1.8 g.) being-a mixtureof thalic acid. Some trimesic acid, calculated to weigh 42 g., remained in the aqueous solution. Conversion of isodurene was'100'% complete. The'total amountof trimesic acid formed was 11.55 g. (0.055 mol), whilethat of mixed phthalic acids (isophthalic and terephthalic) was 15.75 g. (0.09 mol), these amounts corresponding to a yield of 28.3 mol percent of the theory for trimesic acid and 48.7 mol percent for mixed isophthalic and terephthalic acids.

It is often preferred to obtain the desired trimesic acid by employing for the 'hereinbefore described oxidation organic acid mixtures formed'by. a partial oxidation of isodurene in a known manner, for instance, using air oxygen, at temperatures and'pressures and in the presence of catalysts, described in the art. Such product mixtures contain substantial proportions of alkyl-substituted benzene carboxylic acids having at least one carboxyl substituent on the benzene nucleus of each molecule'of these acids, which may be any of the several monobasic isodurylic acids, etc. Salts prepared by neutralizing these organic acid product mixtures, being more soluble in water than isodurene, can be successfully em- .ing sulfur at a valence below plus 6, and, (3) water to yield an vorganicacid product containing a substantial proportion of trimesic acid. Thistwo-stage operation is EXAMPLE II Isodurene (258.8 g.) was subjected to a partial oxidation ina glass turbo-reactor'at a temperature of 260 F. underatmospheric pressure, and in the presence of 0.2 g. of cobalt naphthenate oxidation catalyst,'by feeding through the isodurene charge a stream of air at a rate of"69.3 liters per hour. The reaction was'interrupted in 2 hrs. 40 min. The'oxidate was extracted with caustic under such conditions as tominim'izesaponification of the neutral ester fraction. The final partial oxidation product was predominantly a mixture of sodium salts of. monobasic trimethyl benzoic (isodurylic) acids weighing 76.3 g., which figure corresponded to a yield of aromatic acids of about 66.3%.

This isodurylic acidproduct was then converted by a conventional technique, employing dilute ammonia, to the ammonium salt, and a 46.8 g. charge of the resulting ammonium isodurylate was placed into the same autoclave as in Example -I together with 77 g. of ammonium sulfate, 10 g. of hydrogen sulfide, and 1000 g. of water. The autoclave was sealed, the temperature raised to 625 F. and maintained at this level for one hour. At that time, the pressure on the autoclave read 2425 p. s. i. g. When theheating was-discontinued, and the contents .of the autoclave cooled to room temperature, a

crude acid product weighing 41.3 g. was recovered. It

' new figure corresponding to an overall'yield of trimesic acid equal to at least 23%, the total yield of aromatic acids onthe benzene nucleus in the charging stock. Materials which have been'found effective in theprocess are shown in the following table, where a number of operative combinations of these materials is listed.

Table Elemental sulfur, (NH );SO water Hydrogen sulfide, (NI-1.0 80 water Hydrogen sulfide, Na SO +NH water Hydrogen sulfide, K SO +NH water (NH 8, (NH 80 water (NH4)2SO3; (NH4)2SO4, water (NHQ Sx, (NH SO water (NHQ S, Na SO water tures above about 500 F. and below the critical tem- I perature of water, and preferably at temperatures in the I range from 550 F. to 650 F.

At these temperatures the maintenance of a superatmospheric pressure in the reaction zone is required in order to hold a part of the water in liquid phase. The

pressures employed are usually in the range from about 1000 to 4000 p. s. i. g.

Reaction times from about 30 minuts to about 6 hours may be employed. Shorter reaction times are employed at higher temperatures, and conversely. Long reaction times at the higher temperatures within the above temperature range result in low yields of acidic products and higher conversions of the hydrocarbon material to carbon dioxide and water if an excess of oxidizing agent is present.

The reaction may be conducted either batch-wise as in the tabulated examples or in a continuous manner. A reaction system consisting of a reactor section of 40 feet of stainless steel tubing wound as a coil and immersed in a molten metal bath has been found suitable for conducting the process of the invention continuously at bench scale. The coil is connected to a surge vessel back-pressured with nitrogen gas to maintain suitable operating pressures. Batch oxidations are conducted in a shaker bomb capable of withstanding about 5000 pounds pressure.

Whether the reaction be conducted batch-wise or continuously, the greater portion of the reaction product is recovered in the form of either the salt of a benzene carboxylic acid or in the form of an acid amide. The free acids are readily recovered by heating the reaction product with a strong acid such as sulfuric acid or hydrochloric acid to hydrolyze the amides and ammonium salts. The free acids are then recovered from the acidified reaction product mixture usually by filtration.

Sulfate ion is the effective oxidizing agent in the process of the invention. The oxidation of isodurene proceeds pursuant to the following equation:

In general, a methyl group attached to an aromatic nucleus is oxidized pursuant to the following equation:

Where the alkyl substituent contains more than one carbon atom (as it would be the case of 1,2,3,5-tetraalkyl substituted benzenes in which all four substituents or any one of them may be ethyl, propyl'or butyl radicals having at least one hydrogen atom attached to the Ot-CaI'bOIl), larger amounts of the sulfate oxidizing agent are required to convert the alkyl group to a carboxyl group, as indicated by the following equation:

While ammonium sulfate is the preferred sulfate for use as the oxidizing agent in the process of the invention, other water-soluble sulfates such as sodium sulfate, potassium sulfate, aluminum sulfate, lithium sulfate and ferrous sulfate may be employed.

A relatively small amount of a sulfur compound containing sulfur at a valence below plus 6 should be present in the reaction mixture as a triggering agent or initiator of oxidation if high rates of reaction are to be obtained. It is preferred to employ a small amount of hydrogen sulfide, ammonium sulfide or ammonium polysulfide for this purpose.

The amount of sulfate desirably present in the reac tion mixture is indicated by the equations shown above. It is desirable to employ about 10% molar excess of sulfate over the quantity stoichiometrically required to oxidize the feed.

While the equations do not show water as a material participating in the reaction, the presence in considerable amount is necessary for good conversions and yields. For good operation it is desirable to charge at least 25 mols of water per mol of organic feed to the reaction zone. 30 to mols of water per mol of organic feed usually facilitate good conversions and yields, and even larger quantities of water may be employed if desired. When partial oxidation products are employed for the production of benzene polycarboxylic acids, such as trimesic acid, the amounts of water can be less than those required for the oxidation of polyalkyl benzene hydrocarbons.

The sulfide component of the reaction mixture serves to increase the rate of reaction. The effective oxidizing agent of course is the sulfate ion, but its eflectiveness, especially from the standpoint of rate, is markedly increased by the sulfide. The amount of sulfide charged to the reaction zone is desirably in the range from 0.05 to 0.3 mol per mol of organic compound, and preferably in the range from 0.2 to 0.25 mol per mol of organic feed. These amounts are required to set the reaction under way; as it continues, they will become larger due to the conversion of the sulfate ion to additional sulfide.

Obviously, many and varied modifications of the invention hereinbefore described may be made withoue departing from the spirit and scope thereof.

I claim:

1. A process for oxidizing an organic material selected from the group consisting of isodurene and isodurylic acid to produce a mixture of benzene carboxylic acids containing a substantial proportion of trimesic acid, which comprises: introducing into a reaction zone said organic material, water, a water-soluble sulfate as the oxidizing agent for said organic material, and a minor amount of a water-soluble sulfur compound containing sulfur at a valence below plus 6; and heating the 'reac-' tion mixture to a temperature about 500 F.

2. A process for oxidizing an organic material selected from a group consisting of isodurene and isodurylic acid to produce a mixture of benzene carboxylic acids containing a substantial proportion of trimesic acid, which comprises: introducing into a reaction zone said organic material, water, a water-soluble sulfate as the oxidizing agent for said organic material, and a water-soluble sulfide in an amount from about 0.05 mol to about 0.3 mol per each mol of said organic material; and heating the reaction mixture to a temperature above 500 F.

References Cited in the file of this patent UNITED STATES PATENTS .Naylor Sept. 16, 1952 UNITED STATES PATENT O CERTTFTCATE OF CORRECTION Patent No. 2,876,257 March 3, 1959 William G Tolaxld It is hereby certified that error appears in the-prirflaed specification of the above "numbered patent requiri correction and that the said Letters Patent should read as corrected below. line 7, for about 500 F." read above 500 F of July 1959.

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ROBERT C. WATSON Commissioner of Patents KARL a. AXLINE Attesting Officer 

1. A PROCESS FOR OXIDIZING AN ORGANIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF ISODURENE AND ISODURYLIC ACID TO PRODUCE A MIXTURE FO BEBZENE CARBOXYLIC ACIDS CONTAINING A SUBSTANTIAL PROPORTION OF TRIMESIC ACID. WHICH COMPRISES: INTRODUCING INTO THE A REACTION ZONE SAID ORGAINC MATERIAL, WATER, A WATER-SOLUBLE SULFATE AS THE OXIDIZING AGENT FOR SAID ORGANIC MATERIAL, AND A MINOR AMOUNT OF A WATER-SOLUBLE SULFUR COMPOUND CONTAINING SULFUR AT A VALENCE BELOW PLUS 6; AND HEATING THE REACTION MIXTURE TO A TEMPERATURE ABOUT 500* F. 